At the end of the operating life of a nuclear reactor assembly, the owner is presented with three decommissioning alternatives. Entombment consists of placing the reactor vessel and other parts of the assembly in a sealed condition for an indefinite period of time to allow the ionizing radiation to decay to acceptable levels. At that time the assembly may be modified further or removed. Mothballing consists of placing and maintaining portions of the assembly in protective storage for a period of time before dismantling the assembly. Prompt Removal is the removal of all radioactive components of the assembly without the delays accompanying the entombment and mothballing alternatives.
The most cost-effective alternative has been determined by the nuclear industry to be prompt removal. The nuclear reactor vessel, along with its internal components, comprise the majority of the radioactivity at a shut-down commercial nuclear power facility.
The disposal of spent (used) nuclear reactor fuel in the United States is typically the responsibility of the United States Department of Energy (DOE). The reactor fuel will be transferred to the DOE, independent of the reactor vessel and internals disposal. Therefore, the nuclear reactor will not be packaged and transported with reactor fuel.
In the prompt removal process, the reactor vessel internals have been segmented, removed, and packaged for transportation and disposal in small transportation containers and shielded casks. This requires the handling of components with high curie contents generating high radiation doses. This type of radioactive material must be packaged and transported to satisfy the regulations of both the United States Nuclear Regulatory Commission and the United States Department of Transportation. The packaging and transportation effort is further complicated by the weight of the reactor vessel, typically measured in the hundreds of tons.
Techniques exist to segment the reactor vessel and internals in order to reduce the physical size and curie content of material loaded into licensed transportation containers. These techniques require a substantial amount of underwater cutting and material handling due to the high radiation levels associated with the components.
If the vessel is removed and transported intact without segmenting it as described, risk is involved. The steel reactor vessel is subjected to neutron radiation during the operation of the reactor. This radiation causes a change in the molecular structure of the steel, making it brittle. This embrittlement is a risk to the integrity of the reactor vessel if the vessel is packaged as its own transportation container without a container outside.
This invention is a package containing and protecting the vessel and provides a method of packaging the reactor vessel, with the internal components intact, into a single container, thus reducing the cost of preparation activities and exposure of workers to ionizing radiation. This package, when fitted with external impact limiters and tiedown devices, meets the transportation requirements for a Type B package as defined in Title 10 of the Code of Federal Regulations, Part 71. Additionally, it reduces the total volume of radioactive waste for disposal.
This invention thus eliminates the need to segment the reactor vessel and internals for packaging and transportation, and eliminates the segmentation of portions of the reactor vessel internals into waste which is considered Greater-Than-Class-C. This type of waste is a significant problem, since it is generally not accepted for disposal in near-surface land disposal facilities, the only type of radioactive waste disposal facility currently operating within the United States. This invention reduces the concentration of Greater-then-Class-C waste by averaging the Greater-than-Class-C waste with other materials in the vessel. These reduced concentrations generally allow the package to meet acceptable criteria for burial in near-surface land disposal facilities.